| The longitudinal hydrological connectivity of rivers plays a crucial role in maintaining the health and stability of watershed ecosystems.The climate change in the Yellow River Basin and the construction and operation of water conservancy projects in the middle and upper reaches of the Yellow River have caused changes in the water and sediment conditions in the lower reaches of the Yellow River,leading to changes in the longitudinal hydrological connectivity of the lower reaches of the Yellow River.Therefore,clarifying the magnitude and pattern of the impact of water conservancy project construction and operation on the hydrological connectivity of the lower Yellow River is of great significance in protecting the balance and stability of the ecological system in the region.This article takes the section from Xiaolangdi to Gaocun in the lower reaches of the Yellow River as the research object,and applies remote sensing methods to interpret the rivers,the mid-channel bars,vegetation,and other land features in the study area.After the interpretation,the images are statistically calculated to obtain characteristic parameters such as river area and length,riverbanks size and distribution,vegetation coverage,and analyze the landscape pattern evolution of the rivers under the construction of dams in Xiaolangdi;Considering the impact of landscape pattern index represented by the mid-channel bars,improve the barrier coefficient method for evaluating the longitudinal hydrological connectivity of rivers,and establish a method for evaluating the longitudinal hydrological connectivity of rivers based on landscape pattern effects suitable for a single river section.Use this method to analyze the changes in longitudinal hydrological connectivity of typical sections of the lower Yellow River before and after the construction of the Xiaolangdi Dam,and discuss the impact of water and sediment regulation of the Xiaolangdi Reservoir on the longitudinal hydrological connectivity of the river.The specific results are as follows:The river area and width from Xiaolangdi to Gaocun show a trend of first decreasing and then increasing,while the river length and sinuosity show a trend of first increasing and then stabilizing,and the sinuosity increases significantly;The water and sediment regulation after the construction of the Xiaolangdi dam during the flood season is the main reason for the widening of the river channel.The continuous erosion of the river during the flood season leads to the continuous widening of the river channel,with the most obvious changes in the river from Huayuankou to Jiahetan section;Due to the regulating effect of the Xiaolangdi Reservoir,the oscillation amplitude and frequency of the mid-channel bars have significantly decreased and become stable,leading to a decrease in the degree of aggregation in the river center and a more dispersed distribution in the river center;The longitudinal hydrological connectivity indices of the river before and after the construction of the Xiaolangdi dam were calculated to be 1.35 and 1.5,respectively,indicating a significant improvement in connectivity.The degree of connectivity dispersion decreased over time before the dam was built,while the changes after the dam were more stable;Due to the water and sediment regulation effect of Xiaolangdi,the connectivity during flood season has significantly increased,which is greater than the connectivity before and after flood season;Due to the weakening of river channel oscillation and contraction,the inhibitory effect on vegetation growth is weakened,leading to a gradual increase in vegetation coverage in coastal areas.The research results have enriched the evaluation methods for the connectivity of a single river channel,and have significant scientific value and practical significance in deeply understanding the characteristics and mechanisms of changes in longitudinal hydrological connectivity of rivers. |
